How do I undo a pan?
Blender has many options for viewing the 3D scene.

One of them is probably close to or equivalent or superior to the notion of undo, for some readers, not all readers.

I have focused on Menu Choices below.

I would probably advise you that Blender can provide many good views for you as opposed to a single special view.



Use the numeric keypad with Numlock on to select view orientations such as 

Numpad 1,3,7,9. 

You can do this the control key as well. This will achieve front right top bottom views. Numeric Keypad 

2,4,6,8

rotate the view in known increments.



You can align the view to active, which respects the local axis. You could view the [front] of a model rotated at some unthinkable rotation of 33.5 degrees. Thus you could put a non renderable or renderable object in your scene to recall your perfect view orientation.  

Quad View menu choice is quite useful.

Pressing Numpad . (Numpad Period .) will center the view on the current selection.  If you select 2 or more or all objects with A and then press Numpad . you will get more items in view.

Items can also be selected in the Outliner Window which is sometimes easier.

There are probably 20 similar items I have not mentioned here.